Tenting Vias: What is It and Why is It Done?

Vias are a critical aspect of a printed circuit board. They are the holes you see on a PCB and are what keeps the connection pattern between the layers of a multilayered PCB. Without them, there wouldn’t be that required connection and the PCB wouldn’t work.

Quite often, vias are copper-plated because the material is quite conductive. Depending on the designer of the PCB, the holes may be exposed or covered. When the manufacturer covers the hole completely, it is called either a masked or filled via. If the hole is barely covered, then the manufacturer used a method called tenting.

Many PCB manufacturers prefer the tenting method when placing vias. Covering vias with different material allows them to conduct an electrical signal while dissipating any produced heat. Tenting is not the only method, but it is one that is common amongst PCB designers.

Tenting Vias: What Is It and Why Is It Done?

No matter the size, vias connect each layer of a PCB together. Tenting a via means you create a tent-like shape over the hole to cover the via. The purpose of tenting is to limit the number of exposed conductive pads on the PCB.

When a via is tented, the manufacturer used a solder mask to enclose the opening. Tenting a via has both positive and negative impacts on the PCB. If you’re wondering whether or not you should tent the vias on your PCB, it comes down to the design and manufacturing requirements of your board.

Advantages

Tenting vias has many advantages for a PCB, the first being the protection the solder mask provides to the vias. Just like the solder mask prevents the copper traces from oxidizing and corroding, the solder mask does the same thing for the via. Tenting via creates a barrier that can help prevent any damages to the PCB layers.

Using the tenting method also reduces the number of conductive components that are exposed to external elements. When left exposed, the elements can decrease the integrity of the components and lead to corrosion. It also helps reduce the possibility of a short from happening from solder bridging.

Tenting vias are a cost-effective way of providing protection to the vias and the copper around it. Tenting a via with liquid photoimageable solder mask is the most cost-effective way of tenting.

Disadvantages

Tenting vias is not the most effective method for covering the via. One downside to tenting is that since the solder mask used is liquid, there is the chance of the LPI breaking and creating small holes in the tent. That small hole can trap in moisture and chemicals that can cause corrosion and damage the PCB.

When the PCB is in the prototype phase of the manufacturing process, leaving the vias exposed helps to find any issues with the traces, allowing you to fix and reroute them. Covering the vias could limit the opportunity to find these issues and fix them before it’s too late.

Should You Tent a Via?

Whether or not you tent a via comes down to the design of the PCB and the size of the via. Typically, smaller vias are easier to fill or tent. When the via becomes 15mil in diameter, it ends up being too large for the tenting method.

Tenting vias providing extra protection for the hole and copper elements around it. If left exposed, the outside elements can cause the copper to corrode and damage the PCB. With the tenting method being cost-effective as well, the advantages of tenting a via outweigh the disadvantages.

For via-in-pad technology, non-conductive via fill should be considered.

For more questions about tenting vias and to start manufacturing your PCB, contact us today.